3,4 dichloro-2-furanones as gelatin hardening agents



United States Patent 3,531,292 3,4 DICHLORO-Z-FURANONES AS GELATIN HARDENING AGENTS Salvatore Emmi, Binghamton, N.Y., assignor to GAF Corporation, a corporation of Delaware No Drawing. Filed Sept. 29, 1967, Ser. No. 671,587 Int. Cl. G03c 1/30 US. Cl. 96-111 9 Claims ABSTRACT OF THE DISCLOSURE Delayed action hardening agents for gelatin coating compositions comprising 3,4-dichloro-2-furanones.

The present invention relates in general to the hardening of gelatin and in particular to the hardening of photographic gelatin and gelatino silver halide emulsions to yield compositions having appreciable increase in melting point and good stability on aging with respect to fog, speed and gradation.

In the preparation of photographic gelatin dispersions and gelatino silver halide emulsions, it has been customary practice to treat the dispersion or emulsion at some stage prior to actual coating on a film base with a hardening agent, i.e., a substance capable of reducing the tendency of the gelatin to soften or distend during processing of the photographic material containing the gelatin. The incorporation of hardening agents is for the most part deemed vital in order to provide a laminate element possessed of the requisite structural stability. As will be recognized, many commercial operations such as those associated with high speed photoreproduction may in some instances dictate the use of processing temperatures considerably in excess of those specified for the particular photographic material in question. The published literature, both patent and otherwise, is of course replete with reference to hardening materials which may be employed for the aforedescribed purposes; such compounds include, for example, formaldehyde, hydroxyaldchydes, acrolein, glyoxal and derivatives thereof and mixtures of an aliphatic aldehyde with an aromatic compound containing at least one nuclear hydroxy substituent group such as phenol, resorcinol, resorcylic aldehyde and the like. Although many of the hardening agents of the foregoing type have proved to be effective as regards imparting the desired hardening effects to the gelatin medium containing same, their use is invariably attended by one or more disadvantages. For example, and with reference to the preparation of the light sensitive silver halide emulsion, it is often found that the hardening agents heretofore provided deleteriously affect the sensitometric characteristics of the emulsion leading to the formation of excessive fog, desensitization as well as a general flattening of gradation in the image obtained. "In general, any hardening agents which function by the liberation of formaldehyde will be possessed of the aforedescribed objectionable features as well as that of after hardening.

Consequently, considerable industrial activity has centered around the research and development of hardening agents which would be devoid of any tendency to affect adversely the photographic qualities of the gelatin emulsion. Despite the meritorious achievement in this regard, the overall improvement has proved to be marginal. For example, many of the hardening agents proposed and which purportedly minimize the aforedescribed deleterious effects are capable of exerting hardening effects only upon heating. Unfortunately, the thermal effects resulting from the heating operation are destructive of the protographic properties of the emulsion and especially When the latter is of the high speed type.

3,531,292 Patented Sept. 29, 1970 In certain photographic applications it is of critical importance that each of the gelatin layers present in the photographic element, whether light sensitive or not, be resistant to water at elevated temperatures. This would be the case, for example, with high speed reproduction wherein processing solutions, e.g., developer, fixer, etc. are' of an especially high order of activity. For the most part, those hardening agents considered to be more or less conventional have proved notably deficient for use With emulsions contemplated for high speed processing. In addition, it has been observed that many of the hardening agents specifically devised for high speed processing cause incubation for and/ or undesired after hardening, i.e., cause continuation of hardening of the gelatin during storage. Quite naturally, such properties are highly objectionable and may Well result in development restraint. Moreover, with photographic silver halide emulsions intended for use in the formation of colored images and wherein color coupling compounds are employed for such purposes, interaction of the hardening agent with the color coupling components may be encountered.

It is thus manifestly clear that the advent of high speed process techniques has imposed additional and stringent requirements on the nature of the hardening agent which may be effectively employed. Firstly, it is imperative that the hardening agent be of the delayed action type. i.e., the hardening result does not obtain until actual processing of the photographic emulsion. Any premature hardening action Will, as a practical matter, make emulsion handling extremely difficult if not impossible. This will be readily appreciated since the viscosity increase effected in the gelatin medium tends to vitiate any possibility of obtaining a uniform coating of the desired properties. Secondly, and in view of the rather severe processing conditions characterizing high speed processing, it is absolutely imperative that the hardening agent be capable of exerting significant hardening effects whereby to render the gelatin layer containing same structurally stable and thus impervious to the effects of such conditions. Any defect in structural integrity will, of course, be aggravated by the use of processing conditions involving severe temperatures, solution activity, etc. and in all likelihood render the element unsuitable for commercial use.

Thus, the primary object of the present invention resides in the provision of hardening agents for incorporation into gelatin coating composition wherein the foregoing and related disadvantages are eliminated or at least mitigated to a substantial extent.

Another object of the present invention resides in the provision of hardening agents for gelatin coating compositions contemplated for use in the preparation of photographic silver halide emulsions, said agents providing a delayed hardening action, i.e., the viscosity-increasing effects imparted by such compounds are not evident until processing of the exposed emulsion.

A further object of the present invention resides in the provision of hardening agents beneficially adapted for use with gelatin silver halide emulsions, said agents being totally devoid of any tendency to deleteriously affect the emulsion properties such as fog, speed, contrast, density and the like.

Other objects and advantages of the present invention will become apparent hereinafter as the description proceeds.

The attainment of the foregoing and related objects is made possible in accordance with the present invention which in its broader aspects includes the provision of novel, delayed action hardening agents selected from the group consisting of (a) 5-amino-3,4-dichloro-2-furanones, (b) 5-alkoxy-3,4-dichloro-2-furanones and (c) S-arylacyl- 3,4-dichloro-2-furanones.

The furanone derivatives included by the foregoing definition, although encompassing a relatively broad class of compounds, are nevertheless capable of providing optimum delayed action hardening effects. Particularly beneficial results are obtainable with compounds which, for convenience, may be represented according to the following structural formulae:

wherein R and R represent, independently, hydrogen; alkyl, e.g., methyl, ethyl, propyl, isopropyl, butyl, amyl, etc.; carbalkoxy, e.g., carbethoxy; with the provision that at least one of R and R represent a substituent other than hydrogen; or together represent the non-metallic atoms necessary to form a or 6-membered heterocyclic ring, e.g., ketopyrrolyl; R represents lower alkyl, e.g. methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert. butyl, amyl, and R represents aryl.

Compounds of the type included by the definition given for (a) may be readily prepared by mixing equal molar quantities of mucochloric acid and a suitable amine derivative in toluene in the presence of an acid catalyst. This mixtureis then refluxed until water no longer collects in the attached Dean-Stark trap. The toluene solution is then treated with charcoal, filtered and evaporated until the product begins to crystallize out. Recrystallization is carried out by employing suitable solvent mixtures; e.g., water-ethanol.

Specific representatives of the compounds of this type include, without necessary limitation, the following:

3,4 dichloro 5 aminocarbethoxy-2furanone (M.P. 100103 C.)

3,4 dichloro 5 (N 2 ketopyrrolyl) 2 furanone (.M.P. 176 C.)

Compounds of the type included by the definition given for (b) may be prepared by the procedure described by D. T. Mowry, J. Am. Chem. Soc., 72, 2535 (1950) for methyl ester of mucochloric acid.

As a specific example of the compounds of this type there may be mentioned the following: 3,4-dichloro-S-isopropoxy-Z-furanone (2-isomers-major isomer B.P. 110 C. at 3 mm.)

C1 or 4 3,4 dichloro 5 n butoxy 2 furanone (B.P. C. at 0.5 mm.)

Compounds of the type included by the definition given for (0) may be readily prepared according to the methods described by D. T. Mowry, J. Am. Chem. Soc., 75, 1909 1953 A specific example of this type of compound includes: 3,4 dichloro 5 phenacyl-Z-furanone (M.P. 117-9" C.)

The hardening agents of the present invention may be advantageously employed in any of the layers normally associated with light sensitive photographic elements and consisting wholly or partly of gelatin, Whether or not such layer be light sensitive. As will be appreciated, the urgency surrounding the obtention of satisfactory structural stability exists with regard to non-light sensitized layers as well. Thus, the hardening agents described herein may be incorporated into any of the auxiliary layers containing significant quantities of gelatin such as an anti-hilation layer, anti-abrasion or anti-static layer, and/or subbing layer. The layer embodiment is found to provide a significant measure of improvement in overall structural stability since the presence of the hardening agent tends to augment considerably the primary function of the subbing layer, namely, the promotion of adhesion between the support and subsequently applied layers.

The 3,4-dichloro-2-furanone hardening agents may be added to the gelatin solution and/or light sensitive silver halide emulsion at any convenient stage of the preparation. For example, they may be added shortly prior to coating the gelatin medium onto a suitable support, such as glass, paper, cellulose, cellulose derivative, or any other suitable material conventionally employed as supports in the preparation of photographic elements.

Alternatively, the hardening agents may be incorporated subsequent to coating of the gelatin medium onto the base material, e.g., by immersing the film element in a solution of the hardener. The development of optimum characteristics quite obviously will depend upon the selection of conditions of temperature, time of immersion, concentration of pH, these values being capable of ready determination in a particular instance.

The amount of hardening agent actually incorporated into the gelatin coating composition will depend primarily on the increase in melting point desired. Thus, it has been found that substantial increases in melting point may be obtained by adding amounts of furanone derivative sufficient to yield a hardener concentration within the range of from about .005 part to 0.2 part per part of dry gelatin on a weight basis. The foregoing concentration limitations are significant solely from the standpoint that they assure realization of optimum hardening effects. It will thus be understood that departures from such ranges may be dictated in a particular circumstance, depending upon the requirements of the processor.

The following examples are given for purposes of illustration only and are not to be considered as constituting a limitation on the present invention.

EXAMPLES 1-5 In order to ascertain the effect of varying pH values upon the capacity of the hardening agents to exert delayedaction effects upon the gelatin material, a number of samples were prepared and subjected to immersion treatments, simulating developing conditions. The results of these tests are summarized in the following table.

In each instance, the procedure observed is as follows: Melting point evaluations are taken three days after application of the gelatin coating composition in question to the film base material and after the pH of the coating composition had been adjusted to preselected value. This is accomplished by placing the various samples in water, gradually raising the water temperature and recording the melting point as that temperature at which the gelatin composition disintegrates, detaches or otherwise separates from the film base. Melting point evaluations are taken not only subsequent to immersion in alkaline media but also without such pretreatment. As hereinbefore stated, gelatin coating compositions containing the hardening agents of the present invention are uniquely and advantageously adapted for use in connection with the fabrication of light sensitive photographic film elements of the gelatin silver halide type. As is well known, photographic development of such film samples is effected by the use of aqueous alkaline media in order to accomplish visible image formation. The latter occurs due to deposition of silver. Thus, the alkaline immersion period in the examples corresponds substantially to a typical period required for photographic development under similar conditions, this procedure affording a rather accurate analysis of the extent of gelatin hardening.

furanone.

4. A composition according to claim 1 wherein said furanone comprises 3,4-dichloro-S-isopropoxy-2-furanone.

5. A composition according to claim 1 wherein said furanone comprises 3,4-dichloro-5-n-butoxy-2-furanone.

6. A composition according to claim 1 wherein said furanone comprises 3,4-dichloro-5-phenacyl-2-furanone.

TABLE Co. of 0.2M/ solution Ml. (before immer- M.P. (after 2-3 minin acesion in alkaline meutes immersion in alkatone/igp dium, C. line medium, 0.

g. 8 Ex. No. Hardener ge l pH 5 pH 6 pH 7 pH 5 pH 6 pH 7 1 Control 37 37 2.-. 3, 4-dicl1lor0-5-amino-earbethoxy-2-iuranone 5 40 41 5G 39 85 85 3 3, 4-dichloro-5(N-2-ketopyrollyl-Z-iuranone 5 40 41 87 90 85 85 3, 4-dichloro5-isopropoxy-Z-fnranone. 5 44 70 85 75 85 85 3, 4diehloro-5-phenacyl-Z-iuranonea 5 40 38 41 55 60 59 3, 4-(lichlor0-5n-butoxy-2iuranone 5 39 41 62 85 88 90 As the above-itemized data make manifestly clear, the harden agents of the present invention are eminently capable of imparting significant increases in viscosity to gelatin coating compositions in the presence of an alkaline environment. However, of equal importance is the fact that such hardening effects are not evident until the establishment of a non-acid pH range.

As the above data would likewise suggest, hardening effects in some instances are apparent as the pH of the gelatin emulsion media approaches the neutral range, i.e., in the neighborhood of 7. ,Such a situation poses no particular problems in practice since the pH of the gelatin layer or layers present on the photographic film element is maintained at a value sufiiciently acidic to avoid inadvertent hardening effects.

The furanone hardening agents of the present invention 60 are advantageously adapted for use in formulating gelatin coating compositions intended for use in the fabrication of either black and white or color photographic film elements, or alternatively, elements for difiusion transfer processing, color transfer processing and the like, i.e., processes depending upon the diffusion of silver halide, developer, dye developer, coupler or dye from the light sensitive element to a suitable receiving layer.

This invention has been described with respect to certain preferred embodiments and there will become obvious References Cited UNITED STATES PATENTS 2/1952 Stanton 96111 X 10/1967 Munro 96-111 X NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner US. Cl. X.R. 

